Muslims accept five pillars of the faith: submission to God, prayer, fasting, charity and pilgrimage to Mecca. The two dominant sects split over leadership 1,400 years ago, leading to variations in law, theology and practices:

Sunnis

Shiites

Leadership

Elected by the Muslim community, based on merit and consensus. No special reverence for historic imams. Scholars and legal experts offer non-binding opinions.

Hereditary. Imams directly descended from Ali are revered as infallible sources of religious guidance. Today, mullahs or ayatollahs are arbiters of religious law and practice and lead communal prayers.

Holy cities

Three key cities in the life of Mohammed: Mecca, Medina and Jerusalem

Mecca, Medina and Jerusalem, plus Najaf and Karbala in modern-day Iraq, for their ties to martyred imams.

When Muslim journalist S. Hussain Zaidi toured the USA recently, he was stunned by what he saw: Shiite and Sunni Muslims, whose conflicts have fueled the war in Iraq and tension in the Middle East and beyond, were praying together in U.S. mosques.

"It is something we never see at home," says Zaidi, of India. "They want to kill each other everywhere except in the USA."

For years, Sunnis and Shiites in this country have worked together to build mosques, support charities, register voters and hold massive feasts for Eid al-Fitr (on Oct. 13 this year in the USA), the celebration at the end of the holy month of Ramadan.

Now there are small signs of tension emerging in America's Muslim community that are raising concerns among many of its leaders. They worry that the bitter divisions that have caused so much bloodshed abroad are beginning to have an impact here. Such concerns are rising at a time when the USA's Muslim community has grown from less than 1 million in 1990 to nearly 2.5 million today, with two of three Muslims born overseas, according to a survey by the Pew Research Center.

"You have people who recently arrived from other places where things may have gotten out of hand," says Sheik Hamza Yusuf, the U.S.-born co-founder of the nation's first Muslim seminary, the Zaytuna Institute, in Berkeley, Calif. "It takes just one deranged person with a cousin back home who died in a suicide bombing to create trouble here."

Several recent incidents pointing to rising tension among Sunnis and Shiites here have led Muslim leaders to call on their followers to reach out to those in other sects. None of the incidents has been violent. But Yusuf and other leaders worry that these could be signs of increasingly cool relations between Sunnis and Shiites here or undermine other Americans' views of a religion that has been under particular scrutiny since the Sept. 11, 2001, terror attacks. Among the incidents:

•Shiite mosques and businesses in the Detroit area were vandalized in January, and a Shiite restaurant owner said he'd received a threatening call mentioning his sect.

Authorities have yet to identify the vandals. But some Shiite Muslims told local news media they believe Sunnis were behind the broken windows and graffiti because Shiites had celebrated publicly when former Iraqi leader Saddam Hussein, a Sunni, was executed in December by Iraq's Shiite-led government.

•On several Muslim websites in recent months, Sunnis and Shiites from Seattle to Manhattan have traded accusations that they have been rebuffed from worshiping at each other's mosques.

Meanwhile, a small Sunni group known as the Islamic Thinkers Society, which has branded Shiites as heretics and is known for distributing provocative leaflets in New York's Times Square, has gone online to urge its followers to "avoid" contact with a range of Islamic studies scholars and theologians, several at U.S. colleges.

•Muslim Student Associations on a few campuses, such as Rutgers University in New Brunswick, N.J., and the University of Michigan at Dearborn, have disagreed so vehemently over which sect could lead prayers that students sometimes have refused to pray together.

The factionalism on those campuses has cooled recently, but many observers worry it could return. They say it's partly a reflection of the rising numbers of Muslim students. "If you have nine Muslims in one MSA, they have to get along," says Muslim sociologist Eboo Patel, 31, of Chicago. "If you have 90, there's enough to break into splinter groups."

Other Muslim activists, scholars and imams, who lead the important Friday communal prayers in the nation's 1,000 mosques, agree that the episodes partly reflect their community's growth and diversity in America.

They fear such incidents could fuel "Islamophobia" — their term for irrational prejudice against anyone Islamic.

"The sad reality is that there are extremists" who selectively misuse Islamic teachings to justify their violence, says Ingrid Mattson, a professor of Islamic Studies at Hartford Seminary in Hartford, Conn., and the president of the USA's largest Muslim civic and social group, the Islamic Society of North America.

At the society's annual Labor Day weekend gathering — an event in suburban Chicago that was part academic seminar, part community rally and part reunion for more than 30,000 families — Mattson's keynote speech urged Muslims to "look beyond the seventh-century tribal society into which Islam was first revealed."

A split over succession

Sunnis and Shiites share belief in the five pillars of Islam — submission to God, daily prayer, fasting, charity and a pilgrimage to Mecca at least once in any able Muslim's life. But they split over Islam's spiritual leadership.

The schism dates to the death of the prophet Mohammed in A.D. 632. Shiites believe that a relative, Ali ibn Abi Talib, had been named successor and that his son Ali, assassinated in 661, and grandson Hussein inherited the rightful imam's miraculous knowledge and powers.

Sunnis, however, believed the Muslim community should elect its leader based on scholarly merit, not heredity. They chose Abu Bakr, a companion of the prophet, instead.

By 680, the sects were at war. Hussein was killed at the battle of Karbala in modern-day Iraq that year, and to this day, Shiites mourn him and other martyred imams.

Since then, like Christians who waged religious wars across Europe for centuries over how to interpret the Bible or baptize a believer, Muslim sects and the legal schools within them have developed differing views on faith and practice, each certain that salvation is at stake.

Among the world's estimated 1.4 billion Muslims, about 85% are Sunni and about 15% are Shiite.

For all the conflicts among Muslims abroad, those in America historically not only have gotten along, but assimilated to the point that their sects have become secondary. In a 2006 survey of 1,000 Muslim registered voters, about 12% identified themselves as Shiite, 36% said they were Sunni, and 40% called themselves "just a Muslim," according to the Council on American-Islamic Relations (CAIR).

"America gives people the unique opportunity to leave cultural, historical baggage behind," CAIR spokesman Ibrahim Hooper says. "We can serve as a model to the world of an Islam that is clear, calm, articulate, forthright and civil."

Even so, it's an opportunity a few Muslims in the USA refuse.

"I've seen people fight over how close their toes can be when they kneel in prayer. It's got to stop," says Imam Mohamed Magid of the All Dulles Area Muslim Society (ADAMS), which has seven mosques in the Washington, D.C., area.

ADAMS is primarily Sunni, but Magid has his own way of quelling sectarianism.

"We teach all the scholars and traditions, and we invite Shia and Sunni imams to lead prayers," says the Sudanese-born Magid. "We don't have to fight."

He says he was heartened when 10,000 people at the Islamic Society event cheered for a new Muslim Code of Honor, pledging Sunni and Shiite respect and cooperation.

The code, drafted by the Muslim Public Affairs Council, a civil rights group, initially was circulated in Southern California after the Detroit vandalism incidents. It moved quickly to Michigan and then to the leadership of several major U.S. and Canadian Muslim political, social and religious groups.

In June, a half-dozen groups launched an "American Muslim Iraq Peace Initiative" intended to build harmony and make clear that "America cannot be a scene of conflict," says Nihad Awad, executive director of CAIR.

Move toward 'big-tent Islam'

Besides the efforts to encourage dialogue, there's another phenomenon that could help ward off sectarian friction here: the inexorable force of assimilation.

At a time when rising numbers of American Protestants are attending non-denominational community churches and referring to themselves simply as Christians rather than Baptists, Methodists or Lutherans, a similar thing is happening among Muslims in the USA.

"It's a whole new era," says Patel. "The bulk of the American Muslim community is overwhelmingly young, under age 40. And they are experiencing a huge momentum toward 'big-tent Islam.' "

"We don't want to be defined by the classifications of history and the Middle East. The Quran is our authority," says Salim Al-Marayati, executive director of the Muslim Public Affairs Council. Al-Marayati, a Shiite married to a Sunni, expects to see 10,000 Muslims of all sects celebrate the Eid with the Islamic Center of Southern California next month in Los Angeles.

He calls himself "Sushi," the popular term for a combination of Sunni and Shiite. Once the glib nickname for the children of intermarried couples, it has become shorthand for Muslims who blur sectarian lines.

All that mixing and melding comes to life at the Islamic Society gathering's annual bazaar and the matrimonial meet-up events — the Islamic equivalent of speed dating for singles whose religion bans Western-style dating.

The five-acre bazaar at a convention center in Rosemont, outside Chicago, is a cacophony of blaring music and kaleidoscopic colors, with booths featuring honey, saris, music, travel, bank services, real estate, silver, shampoo, funeral services — and ideas, as well.

There were Sunni and Shiite book stands, promotions for online education programs, and booths for major Muslim political and social groups. Several federal agencies had stands just aisles away from where entrepreneurs hawked T-shirts emblazoned with slogans such as "Frisk Me, I'm Muslim."

At the adjacent Hyatt Hotel grand ballroom, a more familiar form of unity is the focus: marriage.

At each of two "matrimonial events," 200 women, ages 18 and up, were seated at 40 tables, with an empty seat between each woman so 200 men could rotate around the room, chatting with each woman for a few minutes before jumping to the next chair.

Zipping from chair to chair in the ballroom, "I don't think I even had time to ask a girl whether she was Sunni or Shia," says Faizan Arshad, a 24-year-old medical student in Chicago who's discussing a future with a woman he met that day. "To split hairs about sect did not seem the best use of my time," he says in a later e-mail.

Arshad is typical, says Patel, author of Acts of Faith: The Story of an American Muslim. Patel, a Shiite, is married to a Sunni and says they want their "Sushi" child to grow up "fluent in all the multiple rituals and practices of Islam."

Or perhaps Patel's child will be more like Sarah Soliman, 17, of Cincinnati, daughter of Egyptian-born Sunni parents and a conference organizer for the Islamic Society's teen wing, Muslim Youth of North America.

"I didn't know until I was in middle school that there were any differences among us," Sarah says, "and I still don't get the split."

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Sarah Uddin, left, and her mother, Naseem, shop for saris at the Islamic Society of North America's conference, where attendees could buy anything from clothing to Qurans at a huge bazaar.

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